With recent spread of smartphones and tablet PCs and activation of large-capacity multimedia communication, mobile traffic abruptly increases. Mobile traffic increase is expected to double every year. Since most mobile traffic is transmitted through base stations, common carriers are facing serious network load problems. Accordingly, common carriers increase network installation in order to process increasing traffic and commercialize next-generation mobile telecommunication standards for efficiently processing a large amount of traffic, such as mobile WiMAX, LTE (Long Term Evolution), etc. However, other solutions are needed to handle rapidly increasing traffic.
Device-to-device (D2D) communication is a distributed communication technology for directly transmitting traffic between neighboring nodes without using infrastructure such as base stations. In a D2D communication environment, each node such as a terminal finds another terminal physically adjacent thereto, establishes a communication session and then transmits traffic to the other terminal. Since D2D communication can solve traffic overload by distributing traffic concentrated on a base station, it is in the spotlight as a technical element of a next-generation mobile telecommunication following 4G. For this reason, standardization organizations such as 3GPP, IEEE, etc. are promoting D2D communication standards establishment on the basis of LTE-A or Wi-Fi and telecommunication companies such as Qualcomm, etc. are developing independent D2D communication technologies.
D2D communication is expected to improve mobile communication system performance and to create new communication services. Furthermore, D2D communication can support proximity based social network services, network games, etc. Connectivity problems of terminals in shadow areas may be solved using a D2D link as a relay. In this manner, D2D technology is expected to provide new services in various applications.
In reality, machine-to-machine communication schemes such as infrared communication, ZigBee, RFID (radio frequency identification) and NFC (near field communications) based thereon have been widely used. However, these technologies only support communication for special purposes within a very limited distance (1 m or less), and thus it is difficult to categorize the same as D2D communication schemes.
While the concept of D2D communication has been discussed, a method for preventing resource collision with legacy terminals and efficiently allocating resources for discovery signals between D2D devices and a D2D communication request signal has not been studied.